Electrostrictive time-delay signaltranslating device



July 10, 1956 c. J. HIRSCH 2,754,481

ELECTROSTRICTIVE TIME-DELAY SIGNAL-TRANSLATING DEVICE Filed Aug. 9, 1952 UTILIZING -o EQUIPMENT DELAYED-PULSE- PULSE GENERATOR INVENTOR. CHARLES J. HIRSCH ATTORNEY United States Patent .0

ELECTROS CTIVE TIME-DELAY SIGNAL- T SLATING DEVICE Charles J. Hirsch, Douglaston, N. Y., assignor to Hazeltine Research, Inc., Chicago, 11]., a corporation of Illinois Application August 9, 1952, Serial No. 303,628 12 Claims. (Cl. ass-s General This invention relates to electrostrictive time-delay signal-translating devices.

One type of electrostrictive time-delay signal-translating device heretofore proposed has utilized an elongated stress-wave-propagating medium comprising electrostrictive material, such as barium titanate. Such electrostrictive material, however, generally is of a nonhomogeneous structure which causes distortion of the signal translated thereby. Accordingly, to reduce signal distortion there has been proposed a time-delay device comprising an elongated stress-wave-propagating medium of homogeneous metal and including an attached electrostrictive output transducer disposed transversely of the stress-wavepropagating medium, that is, abutting the end of the medium. Such a device has the disadvantage of ordinarily being capable of utilizing only one output transducer because of the large attenuation of the stress wave by the transducer resulting from a high degree of mechanical coupling between the transducer and the stresswave-propagating medium. Also, the attachment of the transducer to the stresswave-propagating medium renders impracticable the provision of adjustable time delays.

It is an object of the present invention, therefore, to provide a new and improved electrostrictive time-delay signal-translating device which avoids one or more of the above-mentioned disadvantages and limitations of such devices heretofore proposed.

It is another object of the invention to provide a new and improved electrostrictive time-delay signal-translating device for faithfully reproducing a translated pulse with an adjustable time delay.

It is another object of the invention to provide a new and improved electrostrictive time-delay signal-translating device for faithfully reproducing a translated pulse with different time delays by means of a homogeneous stress-wave-propagating medium utilizing a plurality of output transducers.

In accordance with a particular form of the invention, an electrostrictive time-delay signal-translating device comprises an elongated stress-wave-propagating medium and an input transducer comprising electrical-signal-input terminals and abutting the aforesaid medium for converting an applied electrical signal to a stress wave. The device also includes an output transducer spaced from the inputtransducer and comprising an electrostrictive element and having a surface abutting the aforesaid medium and disposed approximately parallel to the direction of propagation of the stress wave and having a dimension approximately parallel to the aforementioned direction of propagation approximately equal to an integral odd multiple of one-half wave length of said stress wave for converting the same to an electrical signal.

Also in accordance with the invention, an electrostrictive time-delay signal-translating device comprises an elongated stress-wave-propagating medium. The device 2,754,481 Patented July 10, 1956 includes an input transducer comprising electrical-signalinput terminals and abutting the medium for converting an electrical signal applied to the terminals to a longitudinal-compression wave effective to cause transverse motions of the medium. The device also includes an output transducer unattached to the medium and spaced from the input transducer and comprising an electrostrictive element and having a surface which abuts the medium and is disposed approximately parallel to the direction of propagation of the compresison wave. The output transducer is responsive to the transverse motions of the medium for converting the compresison wave to an electrical signal.

For a better understanding of the present invention, together with other and-further objects thereof, reference is had to the following description taken in connection'with the accompanying drawing, and its scope will be pointed out in the appended claims.

The accompanying drawing is a diagram, partially schematic, of a pulse-translating system including an electrostrictive time-delay signal-translating device represented in diagramamtic view and constructed in accordance with the invention.

Description of pulse-translating system The pulse-translating system represented in the drawing includes an electrostrictive time-delay device 30 constructed in accordance with the invention and comprising an elongated stress-wave-propagating medium 10, preferably of homogeneous metal, such as magnesium, which may be, for example, rectangularin cross section. A flared termination 11 comprising, for example, an alloy of 8 parts bismuth, 4 parts lead, 2 parts tin, and 1 or 2 parts cadmium and known as Woods metal, grips the end of the medium 10 to reduce end signal reflections by absorbing propagated energy.

The time-delay device 30 also includes an input transducer 12 abutting the end of the medium 10 for converting an applied electrical signal to a stress wave and preferably braced against a suitable supporting member 25 for the device 30 shown in fragmentary view. The input transducer 12 preferably includes an electrostrictive elemeat 13 of, for example, barium titanate bonded with a ceramic binder, disposed transversely of the medium 10. The element 13 may be resonant at a predetermined high frequency, for example, 4 megacycles. To this end, the electrostrictive element 13 has a dimension a in the direction of propagation approximately equal to an integral odd multiple of one-half wave length at the resonant frequency. The term integral odd multiple of one-half wave length is meant to include one-half wave length.

The ele-ftrostrictive element 13 has electrical-signalinput terminals preferably comprising conductive strips or films l4, 14, for example, silver strips fused to opposite end faces of the electrostrictive element 13. The element 13 preferably is polarized by the temporary application of a suitable unidirectional potential to the ter minals 14, 14.

The electrostrictive element 13 preferably has a primary signal-responsive dimension disposed longitudinally of the medium 10 for converting an applied electrical signal, which may be an electrical pulse comprising energy of a predetermined frequency, to a longitudinal-compression wave. By primary signal-responsive dimension is meant that dimension corresponding to the direction of polarization, that is, the dimension a between the terminal surfaces 14, 14. The transducer 12 preferably is of approximately the same cross section as the medium 10 and may be bonded thereto in any suitable manner as by a cement applied with heat.

The time-delay device 30 further includes an output transducer 15 spaced from the input transducer 12 and comprising an electrostrictive element 16 having a surface 16a abutting a longitudinal face of the medium and disposed approximately parallel to the direction of propagation of the stress wave for converting the same to an electrical signal. By a surface of the output transducer abutting the stress-wave-propagating medium" is meant a transducer face having a surface area thereof in contact with the stress-wave-propagating medium, as opposed to a transducer face having only an edge thereof in contact with the medium. The time-delay device 30 may include a plurality of output transducers, such as the transducer 17, of construction similar to that of transducer and adjustably spaced by different distances from the input transducer 12 for deriving electrical pulses of adjustable time delays from an applied pulse. The electrostrictive element 16 of the output transducer 15 preferably is resonant approximately at the frequency of the applied signal and has a dimension b of, for example, an integral multiple of one-half wave length of the applied signal.

The electrostrictive element 16 preferably comprises barium titanate bonded with a ceramic binder and polarized transversely of the direction of propagation of the stress wave, that is, in a direction corresponding to the dimension b. The element 16 has on one surface thereof a metallic strip or film,'for example, a fused silver strip 18 comprising an electrical-output-signal terminal or pickoff electrode. The other surface 16a of the output transducer may be similarly silver-coated or may comprise a surface of the electrostrictive element 16, as shown, in which event the abutting surface of the medium 10 serves as another electrical-output-signal terminal of the transducer 15.

The abutting surface 16a of the output transducer 15 preferably has a dimension c approximately parallel to the direction of propagation of the stress wave approximately equal to an integral odd multiple of one-half wave length of the stress wave for reducing undesirable aperture effect, as will be more fully explained hereinafter. The surface 16a has a dimension d transverse to the direction of propagation approximately equal to the corresponding dimension of the medium 10 to provide maximum contact area between the medium 10 and the transducer 15 and yet prevent undesirable vibrations of the transducer 15 which would result if the dimension d were greater than the corresponding dimension of the medium 10.

Means is also provided for adjusting the pressure between the output transducer 15 and the stress-wavepropagating medium 10 and thus the magnitude of the electrical signal derived from the stress wave. This means comprises a suitable clamping mechanism 19, a fragmentary portion thereof being shown in the drawing, including a screw-supported adjustable spring 20 and an attached pressure plate 21.

The pulse-translating system also includes a pulse generator 22 of conventional construction connected to the input terminals 14, 14 of the transducer 12 and which may, for example, generate pulses individually comprising bursts of high-frequency energy. The pulse-translating system further includes suitable delayed-pulse-utilizing equipment 23 connected to the output terminals of the transducers 15 and 17.

Operation of pulse-translating system Considering now the operation of the pulse-translating system, the pulse generator 22 applies to the input terminals 14, 14 of the transducer 12 a pulse of, for example, high-frequency energy at the resonant frequency of the electrostrictive' element 13. The applied pulse causes variations in the dimension a of the element 13 in accordance with the electrostrictive properties thereof. These variations in turn cause the propagation of a longitudinalcompression pulse at the frequency of the applied pulse along the stress-wave-propagating medium 10, as indicated in the drawing by the arrows. Longitudinal compression of the medium 10, represented by facing sets of arrows in the drawing, is accompanied by transverse expansion, in accordance with Poisson's ratio, as represented by the crests of the medium 10. Similarly, longitudinal expansion is accompanied by transverse contraction, as represented by the troughs, one of which is below the transducer 15 in the drawing. The distortion of the medium 10 caused by the compression pulse has been greatly exaggerated in the drawing for the sake of clarity.

The dimension b of the output transducer 15 varies in response to the crests and troughs of the compression pulse over the entire surface 16:: of the transducer 15, as indicated in the drawing. In accordance with the electrostrictive properties of the element 16, the output transducer 15 derives an output pulse representative of the pulse generated by the generator 22 and applies the output pulse to the delayed-pulse-utilizing equipment 23. The output pulse is delayed from the applied pulse by a time interval determined by the stress-wave-propagation velocity of the medium 10 and the distance between the transducers 12 and 15. This time delay may be adjusted as desired by adjusting the position of the transducer 15 along the medium 10.

The pressure at the abutting surfaces of the transducer 15 and the medium 10 controls the degree of mechanical coupling therebetween and, hence, the magnitude of variation of the dimension b of the element 16. Accordingly, the magnitude of the output signal derived by the tra'sducer 15 may be controlled by adjustment of the pressure at the abutting surfaces. Reduction of the pressure generally reduces the magnitude of the output pulse derived by the transducer 15 and, accordingly, reduces the attenuation of the longitudinal-compression pulse caused by the conversion of mechanical to electrical energy accomplished by the transducer 15. Thus, the pressure at the abutting surfaces may be adjusted to cause the transducer 15 to derive an output signal of sufficient magnitude while minimizing attenuation of the compression pulse and thus allow the transducer 17 also to derive a useful output pulse. The transducer 17 responds to the compression pulse in a manner similar to the transducer 15, as indicated in the drawing.

The dimensions of the output transducer 15 are so proportioned as to provide a maximum response for a given contact pressure between the transducer 15 and the medium 10. The proportioning of the dimension b provides a resonant gain of the output pulse derived by the transducer 15, the proportioning of the dimension 0 minimizes aperture effect, and the proportioning of the dimension d provides a maximum contact area between the transducer 15 and the medium 10 for a given dimension 0. The aperture effect just mentioned is caused when the dimension 0 differs from and exceeds an integral odd multiple of one-half wave length of the compression pulse. For example, if the dimension c were an integral even multiple of one-half wave length of the compression pulse, the dimension b would be elongated and compressed at the same time by equal amounts over equal portions of the surface 16a of the transducer 15, resulting in substantially complete output-signal cancellation within the transducer 15. When the dimension c is an integral odd multiple of one-half wave length of the compression pulse, however, the dimension b is not elongated and compressed by equal amonts over equal portions of the contact surface 16a and the transducer 15 then derives a maximumamplitude output signal. For example, when the dimension 0 is equal to one-half wave length of the compression pulse, the stress of the dimension b is in the same sense over the entire surface 16a of the transducer 15 during the peak of each cycle of the compression pulse, as indicated in the drawing, and causes the derivation by the transducer 15 of a maximum-amplitude output signal.

From the foregoing description, it will be apparent that an electrostrictive time-delay signal-translating device constructed in accordance with the invention has several advantages. The device utilizes an input transducer 12 I of a type suited for generating effectively stress waves for propagation and includes a homogeneous stress-wavepropagating medium which causes relatively little distortion of the reproduced electrical signal. The time-delay device 30 also utilizes an output transducer 15 which may be relatively loosely coupled to the stress-wave-propagating medium to derive an output signal of desired amplitude with minimum attenuation of the propagated stress wave, thereby enabling the use of a plurality of such transducers. The time-delay device 30 also has the advantage of providing an adjustable time delay between the input and output pulses.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope ofthe invention.

What is claimed is:

1. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium of homogeneous metal; an input transducer abutting said medium and comprising eleetrical-signal-input electrodes and a polarizable electrostrictive element resonant at a predetermined frequency and having a primary signal-responsive dimension disposed longitudinally of said medium for converting an electrical pulse of approximately said predetermined frequency applied to said electrodes to a longitudinal-compression pulse in said medium; and an output transducer adjustably spaced from and unattached to said input transducer and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said compression pulse and having a dimension approximately parallel thereto and approximately equal to one-half wave length of said compression pulse and a lateral dimension approximately equal to the corresponding dimension of said medium, said output transducer comprising an electrostrictive element resonant approximately at said predetermirnned frequency and polarizable transversely of said direction of propagation and said output transducer being responsive to transverse motions of said medium accompanying said compression pulse for converting said compression pulse to an electrical pulse of adjustable delay from said applied pulse.

2. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium of homogeneous metal; an input transducer comprising electrical-signal-input terminals and abutting said medium for converting an electrical signal applied to said terminals to a stress wave in said medium efiective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and comprising an electrostrictive element and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said stress wave and having a dimension approximately parallel to said direction of propagation approximately equal to an integral odd multiple of one-half wave length of said stress wave, said output transducer being responsive to said transverse motions of said medium for converting said stress wave to an electrical signal.

3. An electrostrictive time-delay signal-translating de' vice comprising: an elongated stress-wave-propagating medium; an input transducer abutting said medium andcomprising electrical-signal-input electrodes and an electrostrictive element resonant at a predetermined frequency and disposed transversely of said medium for converting an electrical signal of approximately said predetermined frequency applied to said electrodes to a longitudinalcompression wave in said medium effective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and comprising an electrostrictive element and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said compression wave and having a dimension approximately parallel to said direction of propagation approximately equal to an integral odd multiple of one-half wave length of said compression wave, said output transducer being responsive to said transverse motions of said medium for converting said longitudinal-compression wave to an electrical signal.

4. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer abutting said medium and comprising electrical-signal-input electrodes and a polarizable electrostrictive element having a primary signal responsive dimension disposed longitudinally of said medium for converting an electrical signal applied to said electrodes to a longitudinal-compression wave in said medium effective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and comprising an electrostrictive element and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said compression wave and having a dimension approximately parallel to said direction of propagation approximately equal to an integral odd multiple of one-half wave length of said compression wave, said output transducer being responsive to said transverse motions of said medium for converting said longitudinal-compression wave to an electrical signal.

5. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical-signalinput terminals and abutting said medium for converting an electrical signal applied to said terminals to a stress wave in said medium effective to cause transverse motions of said medium; and an output transducer adjustably spaced from and unattached to said input transducer and comprising an electrostrictive element and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said stress wave, said output transducer being responsive to said transverse motions of said medium for converting said stress wave to an electrical signal of adjustable delay from said applied signal.

6. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical-signalinput terminals and abutting said medium for converting an electrical signal applied to said terminals to a stres wave in said medium effective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said stress wave and having a dimension approximately parallel to said direction of. propagation approximately equal to an integral odd multiple of one-half wave length of said stress wave, said output transducer comprising an electrostrictive element polarizablc transversely of said direction of propagation and said output transducer being responsive to said transverse motions of said medium for converting said stress wave to an electrical signal.

7. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical-signalinput terminals and abutting said medium for converting an electrical signal applied to said terminals to a stress wave in said medium effective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and comprising a barium titanate element having on one surface thereof a metallic film comprising a pick-off electrode and having another surface abutting said medium and disposed approximately parallel to the direction of propagation of said stress wave and having a dimension approximately parallel to said direction of propagation approximately equal to an integral odd multiple of one-half wave length of said stress wave, said output transducer being responsive to said transverse motions of said medium for converting said stress wave to an electrical signal.

8. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical-signalinput terminals and abutting said medium for converting an electrical signal applied to said terminals to a stress wave in said medium effective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and comprising an electrostrictive A element and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said stress wave and having a dimension approximately parallel to said direction of propagation approximately equal to an integral odd multiple of onehalf wave length of said stress wave and having a dimension transverse of said direction of propagation approximately equal to the corresponding dimension of said medium, said output transducer being responsive to said transverse motions of said medium for converting said stress wave to an electrical signal.

9. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical-signalinput terminals and abutting said medium for converting an electrical signal applied to said terminals to a stress wave in said medium effective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and comprising an electrostrictive element resonant approximately at the frequency of said applied signal and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said stress wave and having a dimension approximately parallel to said direction of propagation approximately equal to an integral odd multiple of one-half wave length of said stress wave, said output transducer being responsive to said transverse motions of said medium for converting said stress wave to an electrical signal.

10. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical-signalinput terminals and abutting said medium for converting an electrical signal applied to said terminals to a stress wave in said medium effective to cause transverse motions of said medium; and an output transducer spaced from said input transducer and comprising an electrostrictive element and having a surface abutting said medium and disposed approximately parallel to the direction of propagation of said stress wave and having a dimension approximately parallel to said direction of propagation approximately equal to an integral odd multiple of onehalf wave length of said stress wave, said output transducer being responsive to said transverse motions of said medium for converting said stress wave to an electrical signal.

11. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical signalinput terminals and abutting said medium for converting an electrical pulse applied to said terminals to a stress pulse in said medium effective to cause transverse motions of said medium; and a plurality of output transducers spaced by different distances from said input transducer and individually comprising electrostrictive elements and individually having surfaces abutting said medium and disposed approximately parallel to the direction of propagation of said stress pulse and individually having dimensions approximately parallel to said direction of propagation approximately equal to an integral odd multiple of one-half wave length of said stress pulse, said output transducers being responsive to said transverse motions of said medium for converting said stress pulse to electrical pulses of different time delays from said applied pulse.

12. An electrostrictive time-delay signal-translating device comprising: an elongated stress-wave-propagating medium; an input transducer comprising electrical-signalinput terminals and abutting said medium for converting an electrical signal applied to said terminals to a longitudinal-compression wave effective to cause transverse motions of said medium; and an output transducer unattached to said medium and spaced from said input transducer and comprising an electrostrictive element and having a surface which abuts said medium and is disposed approximately parallel to the direction of propagation of said compression wave, said output transducer being responsive to said transverse motions of said medium for converting said compression wave to an electrical signal.

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